The present invention relates to an improved device for sensing draft forces for use in a tractor draft control system.
Various mechanisms for sensing draft force have been proposed in the prior art. U.S. Pat. No. 4,271,910 (issued June 9, 1981 and assigned to the assignee of this invention) describes a draft sensor wherein a draft link is coupled to a bracket fixed to a tapered load pin. Twisting of the load pin moves an arm connected to potentiometer type displacement transducer. Such a system suffers from a lack of compactness and its parts are subject to damage due to their exposure at the rear of the tractor. Another type of draft sensor is the parallel plate type which is inserted into the draft link itself. One such sensor is described in U.S. Pat. No. 4,386,533 issued June 7, 1983 and assigned to the assignee of this invention. The operation of such sensors is adversely effected by hysteresis and bending of the draft links. Also, the parts of such sensors must be sized large enough to withstand the total draft force transmitted by the draft link. Another known system includes a strain sensor in a shear pin which is received by the draft links. Use of such a system requires the use of non-standard hitch parts, thus increasing cost.